Overview of Chlamydia trachomatis infection and the requirements for a vaccine.

Chlamydia trachomatis is an important human pathogen. The development of vaccines designed to prevent C. trachomatis-associated morbidity would be highly desirable. In the developing world the major goal is the prevention of blindness due to trachoma; in industrialized societies and in some developing countries, the major goal is the prevention of chlamydial salpingitis and its consequences. In early trials of trachoma vaccine composed of a suspension of elementary bodies (the infectious particles), short-lived protective immunity was induced, but deleterious effects, i.e., hyperreactivity to infection, were also noted. Thus it is likely that separation of the protective from the sensitizing antigens and the development of a subunit vaccine will be necessary. Chlamydial virulence factors include the surface structures (presumably antigenic) that are responsible for specific attachment of the organism to a susceptible host cell, induction of phagocytosis by the host cell, or inhibition of phagolysosomal fusion. Serotype-specific neutralizing antigens might also be candidate antigens. Purification of such subunit antigens from chlamydial particles is probably impractical. It is likely that genetic engineering will be required for the production of cloned antigens after such antigens have been identified.